I updated LMDE today to update pack 4. I'd like to install Mate (package mate-desktop-environment), but all I get from synaptic is

mate-desktop-environment: Depends: mate-core but it is not going to be installed

and if I try to install that a lot of other failed dependencies surface.

Also I'd like to install okular (KDE document viewer), but with similar consequences:

okular: Depends: kde-runtime but it is not going to be installed Depends: libkio5 but it is not going to be installed Depends: libkparts4 but it is not going to be installed Depends: libkprintutils4 but it is not going to be installed Depends: libokularcore1 but it is not going to be installed Depends: phonon but it is not going to be installed

What's going on here? Why can't these dependencies be resolved? The system is up to date, and I have reloaded the repository contents over and over again. They are